In our throughput tests, the 30TB Exos M peaked at 274.44MB/s (512KB block), bang on the official maximum figure. The write performance was actually a little better than the official 275MB/s at 294.98MB/s. However, after peaking, both reads and writes slowly dropped back.
In the read throughput test, the drive peaked at the 512KB block mark at 274MB/s before dropping back to finish the test run at 248MB/s.
In the write throughput test, the Exos X20 peaked at the 8MB block mark at 294MB/s (a little faster than the official maximum) before dropping back slightly to finish the test run at 273MB/s